The present invention relates generally to the field of electrical shielding. More particularly, the present invention relates to a Faraday shield for use with a plasma chamber.
Faraday shields have been used in plasma chambers to reduce capacitive RF coupling, which can result in ion erosion of chamber surfaces. A broad range of chamber materials is susceptible to this ion erosion problem: ceramic, quartz, SiN, SiC, plastics, etc. The Faraday shield is placed between RF antenna coils and the plasma containment chamber and reduces the amount of ion erosion of the chamber that is caused by RF electric field induced ion bombardment. The shield may be either grounded or floating.
A grounded shield design has the down side of making it very difficult to strike a plasma discharge in the chamber because reducing the capacitive coupling also reduces the magnitude of the RF electric field strength. However the grounded shield is effective for reducing ion erosion of the chamber. A floating shield design has the advantage that it does not interfere unduly with striking a plasma. Unfortunately, the floating shield is not very effective at preventing ion erosion of the chamber.
Referring to FIG. 1, an inductively coupled plasma etch reactor implementing a grounded Faraday shield 40 according to the prior art is illustrated. This reactor has a vacuum chamber 10 surrounded by an inductive coil 12. A workpiece 14, usually a semiconductor wafer, is supported inside the chamber 10 on a pedestal 16. An inductive coil antenna 12 is wound around the outside of the chamber 10 and connected to a radio frequency (RF) power generator 18 through an impedance matching network 20 to provide RF power into the chamber. The chamber walls 30 in proximity to the antenna coil are composed of an electrically insulating material, typically quartz or ceramic, so as to minimize attenuation of the RF power coupled into the chamber 10. Etchant gas is introduced into the chamber 10 through gas injection ports 26. A vacuum pump (not shown) evacuates the chamber 10 to a desired chamber pressure.
The chamber dome 30 functions as an RF aperture. The Faraday shield 40 is effective at reducing process induced sputtering of the chamber dome 30. The Faraday shield 40 is connected to ground potential and is, thus, fully grounded.
Referring to FIG. 2, an inductively coupled plasma etch reactor implementing a floating Faraday shield 40xe2x80x2 according to the prior art is illustrated. The floating (or xe2x80x9cisolatedxe2x80x9d) Faraday shield 40xe2x80x2 is a known alternative to the fully grounded embodiment of FIG. 1. This approach is in widespread use on plasma chambers. Its performance is limited in comparison to what is achievable with a grounded design however.
These prior art Faraday shields 40, 40xe2x80x2 reduce parasitic capacitive coupling between the antenna coils of inductively coupled plasma (ICP) sources and the contained plasma. The prior art shields are of a fixed efficiency design however.
Thus, what is needed is a Faraday shield that provides the efficiency of a fully grounded configuration, but that will not create the arc attenuation of a fully grounded configuration.
According to prior art nomenclature, the Faraday shield structures used in conjunction with a processing chamber have been referred to as a xe2x80x9cvoltage distribution electrodexe2x80x9d (or VDE). However, because of significant structural distinctions, it may not be appropriate to use this older terminology for describing at least some embodiments according to the present invention.
One aspect of the present invention is reduction of the intensity of damaging ion-bombardment for certain semiconductor processing chamber surfaces, without affecting plasma striking capability.
Another aspect of the present invention is to provide a Faraday shield having a variable shielding efficiency.
Yet another aspect of the present invention is to control the rate of transition of a Faraday shield between fully ungrounded and fully grounded states.
Still another aspect of the present invention is to control the rate of transition of a Faraday shield of a plasma reactor between a fully ungrounded state and a fully grounded state so as to maintain stable plasma conditions in the transitional period.
A further aspect of the present invention is to control the time rate of change of the change in shielding efficiency of a Faraday shield at a predetermined rate.
An additional aspect of the present invention is to control the time rate of change of change of shielding efficiency of a Faraday shield of a plasma reactor conditioned upon successful matching as the shield efficiency settings change.
Another aspect of the present invention is to provide a variable efficiency Faraday shield having radial symmetry with pie shaped shield segments.
Some of the above aspects are embodied by a shield that provides electrical shielding at a variable efficiency. The shield includes a substrate, a common node disposed on the substrate, and plural shield segments spaced apart from one another and being disposed on the substrate. The shield also includes plural switches, wherein each of the plural switches is connected between the common node and a respective one of the plural shield segments, so that closure of the switch connects its respective one of the plural shield segments to the common node.
Others of the above aspects are embodied by a shielding system that provides electrical shielding at a variable efficiency. The shield includes a substrate, a common node disposed on the substrate, and plural shield segments spaced apart from one another and being disposed on the substrate. The shield also includes plural switches, wherein each of the plural switches is connected between the common node and a respective one of the plural shield segments, so that closure of the switch connects its respective one of the plural shield segments to the common node. The control interface includes a ground circuit connecting the common node to ground potential, and an incremental command circuit connected to each of the plural switches and generating command signals to selectively close the plural switches based upon occurrence of one or more conditions precedent.
Certain of the above aspects are embodied by a plasma reactor which is useful in applying energized plasma to semiconductor articles. The plasma reactor includes a reactor body (where at least a portion of the reactor body is formed of a dielectric material), an RF antenna disposed adjacent the reactor body, an RF matching network connected to the RF antenna to couple energy to the RF antenna, and a shield having variable shielding efficiency, disposed between the RF antenna and the reactor body. A semiconductor article disposed in the reactor body is processed by plasma that is energized by the RF antenna.
Some of the above aspects are embodied by a method of shielding. The shielding method includes providing a shield having a variable shielding efficiency, setting the shielding efficiency at a minimum value, and incrementally increasing the shielding efficiency of the shield.
Some of the above aspects are also embodied by a method of etching a semiconductor article. This method includes placing the semiconductor article in a plasma etch chamber and setting the shielding efficiency of a shield to a minimum value. A plasma is struck about the semiconductor article, and the shielding efficiency of the shield is then increased from the minimum value to a maximum value.
Another way of embodying some of the above aspects is a method of retrofitting a variable efficiency electrical shield to a semiconductor process chamber surrounded by an RF antenna. This method includes providing a variable efficiency electrical shield, installing the shield between the process chamber and the RF antenna, and interfacing the shield to a process controller to establish control of the efficiency of the shield.
Also according to the various embodiments of the present invention, the rate of transition between fully ungrounded and fully grounded states is controllable so as to maintain stable plasma conditions in the transitional period. With this novel approach, the time rate of change of the shielding efficiency is controlled at a predetermined rate once plasma strike is achieved, or is made conditional to successful matching at the previous shield setting.